In the technical area of cutting tools for metal machining, the usage of CVD coatings is a well-known method to enhance the wear resistance of the tool. CVD coatings of ceramic materials such as TiN, TiC, TiCN and Al2O3 are commonly used.
The knowledge of the wear resistance of Al2O3 coatings has increased during the years and properties of different Al2O3 coatings have been studied in detail in several disclosures.
κ-Al2O3 coatings are different from α-Al2O3 coatings in that the crystal structure differs. α-Al2O3 coatings are known to provide a high crater wear resistance in metal cutting in for example ball bearing steel, while κ-Al2O3 coatings are known to be less performing in such an application. κ-Al2O3 coatings are on the other hand known to perform in for example stainless steel.
EP0753602 A1 discloses a cutting tool comprising a κ-Al2O3 coating with a preferred crystal growth orientation in the <2 1 0> direction, which tool exhibits increased wear properties in machining of ball bearing steel.